I don't see any reason why the default out-of-the-box Android experience couldn't be as good or better than the iPhone. The vast majority of people won't root, or use custom ROMs, or maybe even add widgets. The power and flexibility of Android would be even BETTER if it's default implementation was awesome. Haven't people learned from Apple?!
The S4 still commands a great price on craigslist. Keep it in pristine shape then sell it to get the One or trade it.
A female friend of mine got the S4 a week before me, and I talked to her yesterday and looked at her phone. She hadn't customized anything, other than install a few apps. She didn't even know widgets existed!
I haven't heard an official release date on the HTC One for Verizon yet. I have 5 days to return my S4, so that's not going to work. And I'm not going to buy it full price! So I don't think it's going to be an option, unfortunately.